Cheal Kim

Salicylimine-Based Fluorescent Chemosensor for Aluminum Ions and Application to Bioimaging

In this study, an assay to quantify the presence of aluminum ions using a salicylimine-based receptor was developed utilizing turn-on fluorescence enhancement. Upon treatment with aluminum ions, the fluorescence of the sensor was enhanced at 510 nm due to formation of a 1:1 complex between the chemosensor and the aluminum ions at room temperature. As the concentration of Al(3+) was increased, the fluorescence gradually increased. Other metal ions, such as Na(+), Ag(+), K(+), Ca(2+), Mg(2+), Hg(2+), Mn(2+), Co(2+), Ni(2+), Cu(2+), Zn(2+), Cd(2+), Pb(2+), Cr(3+), Fe(3+), and In(3+), had no such significant effect on the fluorescence. In addition, we show that the probe could be used to map intracellular Al(3+) distribution in live cells by confocal microscopy.

Rational Design of a Structural Framework with Potential Use to Develop Chemical Reagents That Target and Modulate Multiple Facets of Alzheimer's Disease

Alzheimers disease (AD) is characterized by multiple, intertwined pathological features, including amyloid-β (Aβ) aggregation, metal ion dyshomeostasis, and oxidative stress. We report a novel compound (ML) prototype of a rationally designed molecule obtained by integrating structural elements for Aβ aggregation control, metal chelation, reactive oxygen species (ROS) regulation, and antioxidant activity within a single molecule. Chemical, biochemical, ion mobility mass spectrometric, and NMR studies indicate that the compound ML targets metal-free and metal-bound Aβ (metal-Aβ) species, suppresses Aβ aggregation in vitro, and diminishes toxicity induced by Aβ and metal-treated Aβ in living cells. Comparison of ML to its structural moieties (i.e., 4-(dimethylamino)phenol (DAP) and (8-aminoquinolin-2-yl)methanol (1)) for reactivity with Aβ and metal-Aβ suggests the synergy of incorporating structural components for both metal chelation and Aβ interaction. Moreover, ML is water-soluble and potentially brain permeable, as well as regulates the formation and presence of free radicals. Overall, we demonstrate that a rational structure-based design strategy can generate a small molecule that can target and modulate multiple factors, providing a new tool to uncover and address AD complexity.

First success of catalytic epoxidation of olefins by an electron-rich iron(III) porphyrin complex and H2O2: imidazole effect on the activation of H2O2 by iron porphyrin complexes in aprotic solvent.

An electron-rich iron(III) porphyrin complex (meso-tetramesitylporphinato)iron(III) chloride [Fe(TMP)Cl], was found to catalyze the epoxidation of olefins by aqueous 30% H2O2 when the reaction was carried out in the presence of 5-chloro-1-methylimidazole (5-Cl-1-Melm) in aprotic solvent. Epoxides were the predominant products with trace amounts of allylic oxidation products, indicating that Fenton-type oxidation reactions were not involved in the olefin epoxidation reactions. cis-Stilbene was stereospecifically oxidized to cis-stilbene oxide without giving isomerized trans-stilbene oxide product, demonstrating that neither hydroperoxy radical (HOO*) nor oxoiron(IV) porphyrin [(TMP)FeIV=O] was responsible for the olefin epoxidations. We also found that the reactivities of other iron(III) porphyrin complexes such as (meso-tetrakis(2,6-dichlorophenyl)porphinato)iron(III) chloride [Fe(TDCPP)Cl], (meso-tetrakis(2,6-difluorophenyl)porphinato)iron(III) chloride [Fe(TDFPP)Cl], and (meso-tetrakis(pentafluorophenyl)porphinato)iron(III) chloride [Fe(TPFPP)CI] were significantly affected by the presence of the imidazole in the epoxidation of olefins by H2O2. These iron porphyrin complexes did not yield cyclohexene oxide in the epoxidation of cyclohexene by H2O2 in the absence of 5-Cl-1-MeIm in aprotic solvent; however, addition of 5-Cl-1-MeIm to the reaction solutions gave high yields of cyclohexene oxide with the formation of trace amounts of allylic oxidation products. We proposed, on the basis of the results of mechanistic studies, that the role of the imidazole is to decelerate the O-O bond cleavage of an iron(III) hydroperoxide porphyrin (or H2O2-iron(II) porphyrin adduct) and that the intermediate transfers its oxygen to olefins prior to the O-O bond cleavage.

A single colorimetric sensor for multiple target ions: the simultaneous detection of Fe2+ and Cu2+ in aqueous media

This study demonstrates the design, synthesis and sensing properties of a simple and efficient chemosensor 1 (1 = 2,6-bis((2-(((pyridine-2-yl)methylamino)methyl)phenol)ethylamido)pyridine) to rapidly detect Fe2+ and Cu2+ in aqueous solution (bis-tris buffer/DMF (8/2, v/v)), exploiting UV-vis spectral analysis, naked-eye and paper devices. The sensor 1 showed significant absorption spectra at 455 nm for Fe2+ and 660 nm for Cu2+, which are responsible for color changes due to the metal-to-ligand charge-transfer. The binding modes of 1 with Fe2+ or Cu2+ have been investigated by Job plot and ESI-mass analysis. In addition, the sensor 1 could be recyclable simply through treatment with a proper reagent such as EDTA. Moreover, the sensor has been used in the development of practically viable colorimetric kits.

A diaminomaleonitrile based selective colorimetric chemosensor for copper(II) and fluoride ions

A new and simple colorimetric receptor 1, based on 2,3-diaminomaleonitrile and julolidine moieties, has been synthesized and characterized. 1 showed a selective colorimetric sensing ability for copper(II) ions by changing color from yellow to colorless, and could be utilized to monitor Cu2+ over a wide pH range of 4–12. The detection limit of 1 (2.1 μM) for Cu2+ ions is much lower than that recommended by WHO in drinking water (30 μM). Moreover, the receptor 1 can also detect fluoride by color change from yellow to orange, distinguishing the fluoride ions effectively from anions such as CH3COO− and CN−. It was also found that the 1–F− complex was reversibly bound and could be simply reverted back through treatment with a proper reagent such as HCl. The sensing mechanism for F− was theoretically supported by DFT and TD-DFT calculations.

Stereoselective alkane hydroxylations by metal salts and m-chloroperbenzoic acid

Abstract Simple metal (M=Mn, Fe, Co) perchlorates associated with m -chloroperbenzoic acid are able to conduct stereoselective alkane hydroxylations via a mechanism involving metal-based oxidants; the catalytic activity of the metal salts is in the order of Co(ClO 4 ) 2 >Mn(ClO 4 ) 2 >Fe(ClO 4 ) 2 .

Dual-channel detection of Cu2+ and F− with a simple Schiff-based colorimetric and fluorescent sensor

A simple and easily synthesized colorimetric and fluorescent receptor 1, based on 4-diethylaminosalicylaldehyde moieties as a binding and signaling unit, has been synthesized and characterized. The receptor 1 has a selective colorimetric sensing ability for copper (II) ion by changing color from colorless to yellow in aqueous solution, and could be utilized to monitor Cu(II) over a wide pH range of 4-11. In addition, the detection limit (12μM) of 1 for Cu(2+) is much lower than that (30μM) recommended by WHO in drinking water, and its copper complex could be reversible simply through treatment with a proper reagent such as EDTA. Moreover, receptor 1 exhibited both a color change from colorless to yellow and fluorescence enhancement with a red shift upon addition to F(-) in DMSO. The recognition mechanism was attributed to the intermolecular proton transfer between the hydroxyl group of the receptor and the fluoride.

A single chemosensor for multiple analytes: fluorogenic detection of Zn2+ and OAc− ions in aqueous solution, and an application to bioimaging

A new highly selective and sensitive chemosensor 1 for both Zn2+ and OAc− with off–on fluorescence behavior in aqueous solution was developed. The selectivity mechanism of 1 for zinc is based on a combinational effect of the inhibition of excited-state intramolecular proton transfer and CN isomerization, and chelation-enhanced fluorescence. As a practical application, in vitro studies with fibroblasts showed fluorescence in the presence of both the receptor 1 and Zn2+. Moreover, the deprotonated 1 can behave as a chemosensing system for turn-on detection of OAc− in preference over various other anions tested. Therefore, 1 can serve as ‘one sensor for multiple analytes’.

Janus-faced Sestrin2 controls ROS and mTOR signalling through two separate functional domains

Sestrins are stress-inducible metabolic regulators with two seemingly unrelated but physiologically important functions: reduction of reactive oxygen species (ROS) and inhibition of the mechanistic target of rapamycin complex 1 (mTORC1). How Sestrins fulfil this dual role has remained elusive so far. Here we report the crystal structure of human Sestrin2 (hSesn2), and show that hSesn2 is twofold pseudo-symmetric with two globular subdomains, which are structurally similar but functionally distinct from each other. While the N-terminal domain (Sesn-A) reduces alkylhydroperoxide radicals through its helix–turn–helix oxidoreductase motif, the C-terminal domain (Sesn-C) modified this motif to accommodate physical interaction with GATOR2 and subsequent inhibition of mTORC1. These findings clarify the molecular mechanism of how Sestrins can attenuate degenerative processes such as aging and diabetes by acting as a simultaneous inhibitor of ROS accumulation and mTORC1 activation.

A colorimetric chemosensor based on a Schiff base for highly selective sensing of cyanide in aqueous solution: the influence of solvents

A new highly selective colorimetric chemosensor 1 (E)-9-(((2-hydroxy-5-nitrophenyl)imino)methyl)-2,3,6,7-tetrahydro-1H,5H-pyrido[3,2,1-ij]quinolin-8-ol for CN− was developed. Receptor 1 showed exclusive response toward cyanide by a color change in aqueous solution. However, in aprotic solvents and methanol, the unique selectivity of 1 for CN− disappeared, and its nonselective color change was observed for other anions. This phenomenon could be possibly explained by the combination of the basicity and the hydrogen bonding ability of the anions. Moreover, 1 could be used as a practical, visible colorimetric test kit in an aqueous environment.